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Good Morning,

We have a business environment in which we have 3 Cisco 3850 PoE stacked and We manage our DHCP through our DC server.

Last weekend our UPS had a failure and switched off all outputs, so all the equipment has been reset since then.

On Monday I started noticing that first, I lost ping to a card reader that had been working fine until now. And sencond and most important: every new computer we plug into our network resolves DHCP fine but has no ping to our GW.

So here's what I know:

  • DHCP requests go through just fine, I can see the new computer's records in our DHCP server.
  • Ping works fine to other computers in the same Vlan/subnet, but I get 0 response from the Gateway
  • With wireshark I could see that these computers spam ARP packets asking for our Gateway with 0 response
  • I flushed my own ARP cache and I actually got a response from the ARP request first try
  • If I use an USB network card from another computer that was already working, it works no problem, until today for some reason
  • The MAC table in the switch has been flushed already
  • Wi-Fi works OK, we have it on a different Vlan but similar setup with the same DHCP server.

Any ideas? I googled the hell out of it and I found no one with the same issue.

Thanks in advance!

  • Is the DHCP scope handing out the address for the Gateway to new machines? – Davidw Jul 30 '18 at 14:17
  • Yes it is. Its giving the correct address. – Arheisel Jul 30 '18 at 14:19
  • Is inter-vlan routing working? – Davidw Jul 30 '18 at 14:31
  • Yes, we wouldn't have DHCP or File Services otherwise – Arheisel Jul 30 '18 at 14:34
  • Aside from the card reader, are computers other than the new computers affected? – Davidw Jul 31 '18 at 7:07
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We had what sounds like the same issue. Drove us crazy for 3 months. Turned out it was some sort of fast networking setting in the bios

  • Any update on the situation? – Robert Cotterman Sep 3 '18 at 2:27
  • Sadly, no. For all I can say it stopped on it's own, but priorities shifted after a short while and we never looked at the issue again. Turns out the switches lost a small change on the power cycle, but that only solved the card reader problem that ended up being a wrong Vlan. – Arheisel Sep 12 '18 at 12:40

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